8 results on '"Urbani, S."'
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2. What Controls Sill Formation: An Overview From Analogue Models
- Author
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Sili, G., Urbani, S., and Acocella, V.
- Abstract
Understanding the mechanisms of shallow magma storage (less than ~10‐km depth) is crucial to defining volcanic plumbing systems and their effect on volcano unrest. Sills are common structures to emplace shallow magma. Many factors may control sill emplacement, but their relative importance has not been evaluated so far. To define a hierarchy among a selection of the proposed factors, we performed analogue models by injecting water at constant flux (magma analogue) within gelatin (crust analogue), investigating the effects of: interface strength and rigidity contrast between layers, density layering, ratio of layer thickness, compressive stresses, magma flow rate, and buoyancy pressure. Our results show that a strong rigidity contrast (i.e., a stiff layer overlying a weak one) and a higher buoyancy pressure are necessary and sufficient conditions for sill emplacement. Low rigidity contrasts require other contributions (weak interface and compressive stress) to develop sills; however, without rigidity contrast sill formation is always inhibited. These experiments suggest that sill emplacement is primarily controlled by rigidity contrasts and magma buoyancy pressure; the second‐order parameters are lateral compression and weak interfaces; the third‐order parameters are the ratio of layer thicknesses, magma flow rate, and density layering. These results are in agreement with field observations in Iceland, Tenerife, Utah, and La Réunion, supporting our proposed hierarchy. Understanding what controls a dike to sill rotation is important to improve our knowledge on magma storage in the upper crustWe have defined a hierarchy among selected parameters controlling sill emplacement to understanding shallow magma transferAnalogue models show that high rigidity contrast and magma buoyancy pressure are necessary and sufficient conditions for sill emplacement
- Published
- 2019
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3. What Drives the Lateral Versus Vertical Propagation of Dikes? Insights From Analogue Models
- Author
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Urbani, S., Acocella, V., and Rivalta, E.
- Abstract
Volcanic eruptions are usually fed by dikes. Understanding how crustal inhomogeneities and topographic loads control the direction (lateral/vertical) and extent (propagation/arrest) of dikes is crucial to forecast the opening of a vent. Many factors, including buoyancy, crustal layering, and topography, may control the vertical or lateral propagation of a dike. To define a hierarchy between these factors, we have conducted analogue models, injecting water (magma analogue) within gelatin (crust analogue). We investigate the effect of crustal layering (both rigidity and density layering), topography, magma inflow rate, and the density ratio between host rock and magma. Based on the experimental observations and scaling considerations, we suggest that rigidity layering (a stiffer layer overlying a weaker one) and topographic gradient favor predominantly lateral dike propagation; inflow rate, density layering, and density ratio play a subordinate role. Conversely, a softer layer overlying a stiffer one favors vertical propagation. Our results highlight the higher efficiency of a stiff layer in driving lateral dike propagation and/or inhibiting vertical propagation with respect to the Level of Neutral Buoyancy proposed by previous studies. Understanding what drives the propagation direction of dikes is a crucial step for eruption forecastingAnalogue models show that rigidity layering (stiff layer above a soft layer) and topography dominantly favor lateral dike propagationA stiff layer promotes lateral propagation more efficiently than the Level of Neutral Buoyancy (LNB) by inhibiting its vertical ascent
- Published
- 2018
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4. Propagation and arrest of dikes under topography: Models applied to the 2014 Bardarbunga (Iceland) rifting event
- Author
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Urbani, S., Acocella, V., Rivalta, E., and Corbi, F.
- Abstract
Dikes along rift zones propagate laterally downslope for tens of kilometers, often becoming arrested before topographic reliefs. We use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes, exploring the presence of a slope in connection with buoyancy and rigidity layering. A gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent, e.g., gelatin stiffness contrasts, while antibuoyancy alone may be insufficient to prevent upward propagation. We also observe that experimental dikes become arrested when reaching a plain before opposite reliefs. Our numerical models show that below the plain the stress field induced by topography hinders further dike propagation. We suggest that lateral dike propagation requires an efficient barrier (rigidity) to upward propagation, assisting antibuoyancy, and a lateral pressure gradient perpendicular to the least compressive stress axis, while dike arrest may be induced by external reliefs. Recent diking events along rift zones showed that dikes can propagate laterally for tens of kilometers arresting before reliefsAnalogue models show that topographic lateral pressure gradient and crustal rigidity layering assist lateral propagationNumerical models show that the stress field induced by topography leads to dike arrest
- Published
- 2017
- Full Text
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5. Anatomy of an extinct magmatic system along a divergent plate boundary: Alftafjordur, Iceland
- Author
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Urbani, S., Trippanera, D., Porreca, M., Kissel, C., and Acocella, V.
- Abstract
Recent rifting episodes highlight the role of magmatic systems with propagating dikes on crustal spreading. However, our knowledge of magmatic systems is usually limited to surface observations and geophysical data. Eastern Iceland allows direct access to extinct and eroded deeper magmatic systems. Here we collected field structural and AMS (anisotropy of magnetic susceptibility) data on 187 and 19 dikes, respectively, in the 10–12 Ma old Alftafjordur magmatic system. At a paleodepth of ~1.5 km, the extension due to diking is at least 1–2 orders of magnitude larger than that induced by regional tectonics, confirming magmatism as the key mechanism for crustal spreading. This magma‐induced extension, inferred from the aspect ratio of the magmatic system, was of ~8 mm/yr, lower than the present one. AMS data suggest that most of dikes have geometrically normal fabric, at least at the margins, consistent with prevalent subvertical magma flow and propagation. Diking is the key mechanism for crustal spreadingPrevalent subvertical magma propagation, along divergent plate boundaries, at ~1.5 km depthCrustal spreading in eastern Iceland at 10–12 Ma was slower than present
- Published
- 2015
- Full Text
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6. Stress plays a role in the association between cognitive constructs and measures of eating disorders in male subjects
- Author
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Sassaroli, S., Mezzaluna, C., Amurri, A., Bossoletti, R., Ciccioli, T., Perrotta, A., Romualdi, A., Stronati, A., Urbani, S., Valenti, V., Milos, G., and Ruggiero, G.
- Abstract
Objective:Several theorists have hypothesized that stressful situations may trigger abnormal eating and even eating disorders in predisposed people. The purpose of this study was to assess whether a stressful situation would reveal an association between perfectionism and low self-esteem, and measures of eating disorder symptoms in male high school students. Method: A sample of 61 male high school students completed the Eating Disorder Inventory, the Multidimensional Perfectionism Scale, and the Self Liking and Competence Scale three times: on an average school day, on the day of an exam and on the day the subjects received the results of that exam. Linear regression analysis was carried out to verify whether the dimensions of perfectionism were associated with the measures of eating disorders. Results:Interoceptive awareness was associated with ‘Bulimia’ only during the stressful situation and with ‘Drive for thinness’ both in stress and non stress situations. Other results were contradictory and difficult to interpret. Discussion: The results suggest that in nonclinical male individuals stress might bring out a previously absent association between some psychological predisposing factors for eating disorders and an actual desire or plan for ED related thoughts and behaviours. Such a finding suggests that stress may stimulate behaviours related to eating disorders in a predisposed personality. A central role may be played by interoceptive awareness in male subjects.
- Published
- 2005
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7. Antihypertensive Effect of Spironolactone in Essential, Renal and Mineralocorticoid Hypertension
- Author
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Mantero, F., Armanini, D., and Urbani, S.
- Abstract
1. The hypotensive effect of spironolactone has been studied in twenty-four patients with various forms of hypertension. 2. In essential hypertension a greater fall of blood pressure was achieved in patients with renin activity hyporesponsive to postural change than in those in whom renin responded normally to posture. 3. A poor hypotensive response was observed in patients with renal or renal arterial disease and secondary aldosteronism. 4. The variable hypotensive response seen in patients with primary aldosteronism predicted the response to adrenal surgery. 5. Blood pressure was not lowered by spironolactone in one case of 17-hydroxylation deficiency or in one case of malignant ovarian arrhenoblastoma producing aldosterone.
- Published
- 1973
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8. Interpreting Inverse Magnetic Fabric in Miocene Dikes From Eastern Iceland
- Author
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Trippanera, D., Porreca, M., Urbani, S., Kissel, C., Winkler, A., Sagnotti, L., Nazzareni, S., and Acocella, V.
- Abstract
Anisotropy of Magnetic Susceptibility (AMS) is a valid tool to investigate magma flow direction within dikes. However, geometrically inverse magnetic fabric characterized by maximum magnetic susceptibility axis (kmax) perpendicular to the dike wall may complicate the interpretation of flow trajectories. To better understand the nature of this fabric, we present a multiscale study on 19 dikes (383 samples) in the Miocene Alftafjordur volcanic system (Iceland), where 80% of the samples show a geometrically inverse magnetic fabric. We carried out (1) AMS measurements at different magnetic fields and temperatures, along with Anisotropy of Anhysteretic Remanent Magnetization (AARM) analysis; (2) hysteresis loops and FORC diagrams; (3) thin section analysis; (4) structural fieldwork. A variable Ti‐content (0.1 < x < 0.6, Fe3‐xTixO4) titanomagnetite is the main magnetic carrier, and the contribution of the paramagnetic elongated crystals to the magnetic fabric is negligible. Single domain is not the prevailing domain state of the magnetic particles, suggesting that its occurrence cannot be the main cause for the inverse fabric. AMS analysis at different fields and temperatures along with AARM allow us to exclude any mineral phase change of the titanomagnetite across the dike. Nevertheless, kmax is parallel to a diffuse horizontal column‐like fracture pattern perpendicularly oriented with respect to the dike strike. This suggests that the Ti‐magnetite mineral orientation during dike cooling was affected by the fracture network progressively developing columnar basalts. This study demonstrates that the interpretation of AMS data on old and deep volcanic bodies is not straightforward and observations at different scales are required. Our analyses about the magnetic fabric of the Alftafjordur dike swarm revealed that most of the samples show an inverse magnetic fabricThe origin of the inverse magnetic fabric is associated with the development of horizontal fractures during the cooling stage of dikesIt is not straightforward to infer the magma flow direction on deep and old exhumed dikes by using standard low‐field AMS measurements only
- Published
- 2020
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